In recent years, a technique has been developed for achieving higher data storage density in a phase transition type optical disk, using a blue semiconductor laser and utilizing an objective lens having a high NA of 0.85.
When using the aforementioned technique, even if the diameter of the optical disk is small, for example approximately 5 cm, the capacity of the optical disk is 3 to 4 GB so that an optical disk having a large capacity can be implemented.
By applying a compressing technique such as MPEG2 to the optical disk, it is possible to implement a genuine optical disk video camera which can perform photographing with equivalent picture quality for an equivalent time to those of a conventional tape.
In the optical disk video camera, random access can be given to an optical disk. In contrast to a video camera using a conventional tape, therefore, rewinding is not required so that a user does not need to wait for a rewind operation. Moreover, in the optical disk video camera, a user can immediately reproduce the video intended to be viewed by selecting a thumbnail video. Moreover, the optical disk video camera can store a static image subjected to a JPEG compression on the same optical disk. Therefore, in the above-described optical disk video camera, the camera is expected to be of greater practical use to the user, and more comfortable and convenient.
In a semiconductor laser to be used in an optical disk device such as an optical disk video camera, however, the amount of heat generation per unit volume is generally larger than that in other integrated circuits (IC) and electronic components.
On the other hand, the upper limit of an operation guarantee temperature at which the operation of the semiconductor laser is guaranteed is low, that is, between 60 and 70° C. Furthermore, even if an operating temperature for operating the semiconductor laser ranges within the operation guarantee temperature, the lifetime of the semiconductor laser tends to be shorter when the operating temperature is raised.
Accordingly, a reduction in the consumed power of the optical disk device or an improvement in the radiating mechanism of the optical disk device is greatly desirable, in order to reduce the operating temperature of the semiconductor laser to be mounted on the optical head.
For this purpose, conventionally, there have been various proposals, mainly for a semiconductor laser and peripheral components thereof in relation to the optical disk device. In order to suppress a rise in the operating temperature of the semiconductor laser, basically, it is possible to suggest two approaches. One approach is, a reduction in a consumed power and another is an improvement in a radiating mechanism.
A description will be given of three examples related to improvement in the radiating mechanism.
As an example, Japanese Laid-Open Patent Publication No. 11-112923 has described a configuration in which an optical disk device is surrounded by a frame member capable of easily radiating heat. The device and the frame member are fixed to a frame having a radiating fin and are incorporated in a camera to improve the ability of the optical disk device to radiate heat. The frame member is formed by an elastic material and also serves to protect the optical disk device from vibration.
As another example, Japanese Laid-Open Patent Publication No. 2001-338460 has described a configuration in which heat generated in a semiconductor laser mounted on an optical head is transferred outside of the laser and eliminated by a Peltier element and a cooling fan in order to cool the semiconductor laser. With this configuration, a mechanism section mounting the optical head and a circuit board (a circuit section) are separated from each other and a heat insulating member is disposed between the mechanism section and the circuit board. An effect of providing the heat insulating member is that heat generated in the circuit section is prevented from being transferred to the mechanism section.
As a further example, Japanese Laid-Open Patent Publication No. 2002-15561 has described a configuration in which a radiating plate having a high thermal conductivity is disposed between a mechanism section and a circuit section in an optical disk device. An air layer is formed between the mechanism section and the radiating section in order to improve the radiation ability of the optical disk device. An effect of providing this configuration is that heat generated in the circuit section is not transferred to the mechanism section, but is radiated from the radiating plate, and the temperature of the mechanism section provided with a semiconductor laser is prevented from being raised.
In the case in which the size of the optical disk device is reduced and the size of a video camera incorporating the optical disk device is also reduced, i.e. when manufacturing a small-sized portable video camera or a mobile video camera, all of the aforementioned three examples have the following problems.
In the configuration described in Japanese Laid-Open Patent Publication No. 11-112923, the frame member surrounds the optical disk device. Therefore, the size of the frame member becomes comparatively large.
The Peltier element described in Japanese Laid-Open Patent Publication No. 2001-338460 has a comparatively large power consumption for cooling. Furthermore, an opposite surface to a cooling surface generates heat corresponding to an amount of power consumed by the Peltier element. In addition, the cooling fan also consumes power. Accordingly, taking these factors into account when considering a small-sized portable video camera, a rise in the temperature of the whole video camera is increased. When the Peltier element and the cooling fan are driven for cooling, the duration of a battery used in the camera is reduced due to the increase in power consumption.
In Japanese Laid-Open Patent Publication No. 2001-338460, it can be assumed that the insulating material disposed between the mechanism section and the circuit section is effective because it does not directly transfer the heat generated in the circuit section to the mechanism section.
With this configuration, however, the air in the vicinity of the mechanism section in the optical disk device is exchanged with the air in the vicinity of the circuit section. In this configuration, moreover, the mechanism section and the circuit section are thermally coupled to each other by means of a top cover and a bottom cover which enclose the whole optical disk device.
Accordingly, in the optical disk device, it can be assumed that the transfer of the heat generated in the circuit section, to the mechanism section is temporarily blocked by the insulating member. Also it can be assumed that the temperatures of two covers enclosing the mechanism section and the circuit section are almost equal to each other by the exchange of the air and the thermal coupling of the mechanism section and the circuit section in the case where the optical disk device is used for a long time.
Accordingly, in Japanese Laid-Open Patent Publication No. 2001-338460, it can be predicted that a time required for the saturation of the temperature is prolonged and a saturation temperature is not changed depending on the presence of the insulating member. In other words, in respect of the suppression of a rise in temperature around the semiconductor laser, it can be assumed that the insulating material disclosed in Japanese Laid-Open Patent Publication No. 2001-338460 is effective when the optical disk device is used for a short time and is less effective when the optical disk device is used for a long time.
Moreover, it can be assumed that a great radiating effect can be obtained in the case in which the radiating plate having a high thermal conductivity is disposed between the mechanism section and the circuit section and is directly attached to the case of a personal computer as in Japanese Laid-Open Patent Publication No. 2002-15561. However, the mechanism section and the circuit section are thermally coupled to each other through the radiating plate. A situation might occur in which the amount of heat generation of the mechanism section is smaller than that of the circuit section, and a rise in the temperature of the mechanism section is smaller than a rise in the temperature of the circuit section. As a result of this, the heat generated in the circuit section is transferred to the mechanism section so that the temperature of the mechanism section is raised.
As described above, a conventional radiating mechanism has the effect of preventing a rise in the temperature of the semiconductor laser. However, such a radiating mechanism is not very suitable for small-sized portable equipment or mobile equipment.
In the case in which a blue semiconductor laser is used in the optical disk device and the size of the optical disk device is reduced, the problem of the rise in the temperature becomes even more serious.
As compared with a red semiconductor laser, the blue semiconductor laser, in principle, has a higher forward voltage in operation and an operating current of the blue semiconductor laser is also larger under the existing circumstances. As a result, the amount of heat generation is very large. Accordingly, the blue semiconductor laser itself operates at temperature higher than the temperature of the red semiconductor laser.
In addition to this, the size of the optical disk video camera is set to be equivalent to that of a video camera using a tape. When the size of the optical disk device is reduced, therefore, the surface area of the optical disk device is decreased.
In general, the radiating capability of the optical disk device is almost proportional to the surface area thereof When the surface area of the optical disk device is decreased, the radiating capability of the optical disk device is necessarily reduced. When the consumed power of the optical disk device is set to be constant, accordingly, a rise in temperature in the optical disk device is more increased.
In order to lower the temperature of the blue semiconductor laser to have the same level as the level of the temperature of the red semiconductor laser in such a situation, it is necessary to suppress the rise in the temperature in the optical disk device to a great extent than in the case in which the red semiconductor laser is used. This is one of great problems for a reduction in the size and shape of the optical disk device.
In order to solve the problems described above, it is an objective of the present invention to provide a semiconductor laser device in which rise in temperature therein can be effectively contained.